Effect of some gastrointestinal hormones on antral, small intestinal and caecal myoelectrical activity in the conscious miniature pig

The effect of i.v. infusion of gastrin (CCK-4), cholecystokinin (CCK-8) and pancreatic polypeptide (PP), 20 and 200 ng/kg/min for 1 h, on gastrointestinal electrical activity and arterial pressure was studied in conscious miniature pigs. During infusion of CCK-8 a transient hypertension was observed. In the antrum, the 3 peptides provoked an increase in slow wave activity and a decrease in spike activity. In the intestine, CCK-8 induced an increase in ileal spiking activity, whereas infusion of PP resulted in an increased frequency of long spike bursts in the caecum.

The possible involvement of pancreatic polypeptide in the paracrine regulation of human and rat adrenal cortex

Pancreatic polypeptide (PP) is a member of a family of 36-amino acid brain-gut peptides, including neuropeptide Y (NPY) and polypeptide YY (PYY) and acting through many subtypes of Y receptors belonging to the superfamily of the G protein-coupled receptors. PP was found to increase both glucocorticoid and cyclic-AMP production by dispersed rat and human adrenocortical cells in a concentration-dependent manner. Minimal and maximal effective concentrations were 10(-10) and 10(-8) M, respectively. The glucocorticoid secretagogue effect of 10(-8) M PP was blocked by the protein kinase A (PKA) unhibitor H-89, but not by the ACTH-receptor antagonist corticotropin-inhibiting peptide (CIP) Autoradiography showed the presence of [125I]PP binding sites in the inner zones of rat and human adrenal cortex, which were not displaced by NPY, PYY, ACTH or CIP. Sizable amounts of PP-immunoreactivity were detected in the medulla of both rat and human adrenals (about 50-100 fmol/mg); this content may give rise, upon submaximal stimulation of PP release, to local intraadrenal concentrations of about 10(-8)/10(-7) M. Collectively, these findings allow us to draw the following conclusions: (i) PP stimulates glucocorticoid secretion, acting through specific receptors coupled with the adenylate cyclase/PKA-dependent signaling pathway; and (ii) PP could be included in that group of regulatory peptides, contained in adrenal medulla, which are able to control the secretory function of the cortex acting in a paracrine manner.

Role of the Y5 neuropeptide Y receptor in feeding and obesity

Neuropeptide Y (NPY), a 36-amino-acid neuromodulator abundantly expressed in the brain, has been implicated in the regulation of food intake and body weight. Pharmacological data suggest that NPY's stimulatory effect on appetite is transduced by the G-protein-coupled NPY Y5 receptor (Y5R). We have inactivated the Y5R gene in mice and report that younger Y5R-null mice feed and grow normally; however, they develop mild late-onset obesity characterized by increased body weight, food intake and adiposity. Fasting-induced refeeding is unchanged in younger Y5R-null mice and they exhibit normal sensitivity to leptin. Their response to intracerebroventricular (i.c.v.) administration of NPY and related peptides is either reduced or absent. NPY deficiency attenuates the obesity syndrome of mice deficient for leptin (ob/ob), but these effects are not mediated by NPY signaling through the Y5R because Y5R-null ob/ob mice are equally obese. These results demonstrate that the Y5R contributes to feeding induced by centrally administered NPY and its analogs, but is not a critical physiological feeding receptor in mice.

Pancreatic polypeptide stimulates rat adrenal glucocorticoid secretion by activating the adenylate cyclase-dependent signaling pathway

Pancreatic polypeptide (PP) concentration-dependently raised basal corticosterone and cyclic-AMP production of dispersed rat zona fasciculata/reticularis adrenocortical cells, maximal effective concentration being 10(-7) M. 10(-7) M PP also significantly enhanced submaximally (10[-12]/10[-11] M), but not maximally (10[-9]/10[-8] M) ACTH-stimulated corticosterone and cyclic-AMP release. Corticosterone responses to PP were abolished by the specific protein kinase A (PKA) antagonist H-89 (10[-5] M). The selective ACTH-receptor antagonist corticotropin-inhibiting peptide (10[-6] M) annulled corticosterone response to 10(-9) M ACTH, but not to 10(-7) M PP. Collectively, our present findings indicate that PP stimulates glucocorticoid secretion of rat adrenal glands, acting through specific receptors coupled, like those of ACTH, with the adenylate cyclase/PKA-dependent signaling pathway.

A comparison of actions of neuropeptide Y (NPY) agonists and antagonists at NPY Y1 and Y2 receptors in anaesthetized rats

The pancreatic polypeptide family includes three members, neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP), with sequence homology between members and species varying from approximately 50 to 80%. Some of these peptides were compared in the mammalian cardiovascular system for activity mediated by actions on pre- (Y2) and post-junctional (Y1) NPY receptors. NPY and PYY, with sequence homology of 67% have similar actions on Y1 and Y2 receptors. Rat pancreatic polypeptide (rPP) with sequence homology of approximately 50% is inactive at both. This study reports that the chimeric peptide, hPP1-11/NPY12-36 and the truncated peptide NPY2-36 show similar activity to NPY mediated through both receptor types in vivo, while salmon PYY (sPYY), with 81% homology to NPY, has improved potency at both receptor subtypes. NPY3-36 has equal activity with NPY on actions mediated through Y2 receptors, but significantly reduced activity mediated through Y1 receptors. Two NPY antagonists were also examined: PYX2 was inactive in vivo and 1229U91 showed potent, long-lasting activity on Y1 receptor-mediated effects.

The rabbit ileum: a sensitive and selective preparation for the neuropeptide Y Y5 receptor

The rabbit ileum shows high sensitivity to neuropeptide Y. Relaxations are obtained in this tissue with human pancreatic polypeptide > peptide YY > > [Leu31,Pro34]neuropeptide Y > rat pancreatic polypeptide > human neuropeptide Y in this order of potency that is indicative of a Y5 receptor. Effects of neuropeptide Y and congeners are not affected by neuropeptide Y Y1 receptor antagonist (BIBP 3226), but are reduced by the neuropeptide Y Y5 receptor antagonist JCF 104 (2-(naphtalen-1-yl)-3-phenylpropane-1,2-diamine). Rabbit ilea provide sensitive and selective neuropeptide Y Y5 receptor preparations.

Characterization of the receptor response for the neuropeptide Y-evoked suppression of parasympathetically-mediated contractions in the guinea pig trachea

Neuropeptide Y (NPY) acts via several distinct receptor types. The aim of the present study was to examine which NPY receptors are coupled to inhibition of parasympathetically-mediated contractions of the isolated guinea pig trachea. Electrical field stimulation of tracheal rings evoked a rapid twitch, which was abolished by atropine (1 microM). NPY, the structurally related hormone peptide YY (PYY), the Y2 receptor agonist [Cys2, Aoc5-24, D-Cys27]NPY, as well as NPY 5-36 and NPY 13-36 evoked a concentration-dependent inhibition of the electrically-stimulated twitches. Pretreatment with the Y1 receptor-selective antagonist BIBP3226 (1 microM) failed to prevent the NPY-induced inhibition. Although less potent than NPY, the Y1 (and Y4-Y6) receptor agonist [Leu31, Pro34]NPY also inhibited the electrically-stimulated twitches. Another NPY-related peptide, pancreatic polypeptide, which recognizes Y4-Y6 receptors did not affect the stimulated twitches at concentrations up to 1 microM. However, pretreatment with the Y1 receptor-selective antagonist BIBP3226 (1 microM) virtually abolished the inhibition evoked by [Leu31, Pro34]NPY. None of the peptides affected the baseline tension and BIBP3226 (1 microM) per se did not affect the amplitude of the electrically-stimulated twitches. In conclusion, it seems that NPY and PYY are capable of suppressing parasympathetically mediated contractions in the guinea pig trachea mainly via Y2 receptors, but there is also a small contribution from Y1 receptors.

Effect of pancreatic polypeptide on rat dorsal vagal complex neurons

1. Pancreatic polypeptide (PP) microinjected into the dorsal vagal complex (DVC) elevates gastric activity through a vagal mechanism. Thus, it was hypothesized that PP alters the activity of nuclei comprising the DVC, i.e. the nucleus tractus solitarii (NTS) and the dorsal motor nucleus (DMN). 2. In vivo and in vitro approaches were used. For in vivo studies, micropipettes were used for recording and injecting vehicle or PP. Neurons were identified as NTS or DMN using orthodromic and antidromic activation, respectively, following vagal stimulation. Gastric-related DVC neurons were located using antral inflation. For in vitro studies, DMN neurons were recorded from medullary slices. 3. Of the twenty-eight NTS and DMN neurons identified, fifteen were activated, six inhibited and seven unaffected after PP microinjection. Forty-two gastric-related neurons were located in the DVC, of which twenty-five were stimulated by PP and seventeen exhibited no change. No gastric-related cells were inhibited. 4. For in vitro studies, 66% of DMN neurons were activated by PP (n = 27/47) while the remaining 33% were inhibited (n = 14/47). Similar results were obtained in normal or synaptic blockade media. 5. These results support the hypothesis that PP alters DVC neuronal activity, which may thereby lead to the previously observed alterations in gastric activity.

Motilin is a biosignal controlling cyclic release of pancreatic polypeptide via the vagus in fasted dogs

The mechanism of associated fluctuations in plasma motilin and pancreatic polypeptide (PP) concentrations was studied in fasted conscious dogs while gastric motility was monitored. Plasma motilin and PP concentrations were measured by radioimmunoassay. In intact normal dogs, exogenous motilin (0.03-0.3 g/kg) stimulated dose-related release of PP, but PP did not stimulate motilin release. Motilin-induced PP release was completely inhibited by pretreatment with cholinergic blockers and a 5-hydroxytryptamine3 (5-HT3) receptor antagonist, and by vagotomy. The cyclic release of PP was abolished after vagotomy and duodenectomy. However, PP release stimulated by exogenous motilin was apparent after duodenectomy but not after vagotomy. In conclusion, motilin appears to stimulate PP release via vagal, cholinergic muscarinic pathways involving 5-HT3 receptors and to act as a biosignal controlling PP release by mediating the interdigestive periodic changes in the duodenum to the center of the autonomic nervous system. This represents a new role for motilin.

Inhibition of cyclic AMP-dependent chloride secretion by PP receptors and alpha 2-adrenoceptors in a human colonic epithelial cell line

The effects of a number of agonists which inhibit intestinal chloride secretion were investigated in Colony-1 (Col-1) cells, a subpopulation derived from the HCA-7 human adenocarcinoma cell line. Neither peptide YY (PYY) or somatostatin 14-28 (SRIF) reduced short-circuit current (SCC) in Col-1 epithelial layers stimulated with vasoactive intestinal polypeptide (VIP), suggesting that their respective receptors are either absent in this cell line, or are not functionally coupled. A second member of the neuropeptide Y family, pancreatic polypeptide (PP), decreased VIP-elevated SCC with an EC50 of 25.6 nM. Maximal PP responses were unaffected by prior addition of PYY, indicating that Col-1 cells may express a PP specific, Y4-like receptor. The alpha 2-adrenoceptor agonist clonidine also attenuated VIP-stimulated SCC (EC50342 nM) through the alpha 2A receptor subtype, since clonidine responses were inhibited by yohimbine and rauwolscine but not altered by previous addition of prazosin. Col-1 cells responded to both apical and basolateral addition of VIP or clonidine; to an extent, this lack of sidedness reflects the ability of drugs to permeate through the Col-1 epithelial layers. Both PP and clonidine also inhibited SCC in unstimulated Col-1 cells or those pretreated with 3-isobutyl-1-methylaxanthine (IBMX) or a submaximal concentration of forskolin, agents which both directly elevate intracellular cAMP. After a maximal concentration of forskolin (10 microM), which increased SCC to a significantly greater extent than either VIP or IBMX, the effects of both agonists were negligible. The absence of PP and clonidine responses under these conditions may have implications for the mechanisms by which these agonists inhibit, chloride secretion in Col-1 epithelia. In addition carbachol reduced SCC stimulated by 10 microM forskolin, in contrast to control carbachol responses which consisted of a rapid decrease followed by a transient elevation in SCC; this observation suggests that Col-1 cells may also be a useful model for studying the interactions between Ca(2+)- and cAMP-dependent mechanisms involved in epithelial ion transport.

Several receptors mediate the antisecretory effect of peptide YY, neuropeptide Y, and pancreatic polypeptide on VIP-induced fluid secretion in the rat jejunum in vivo

Several Y receptor subtypes have been cloned and/or pharmacologically characterized that mediate the effects of the regulatory peptides peptide YY (PYY), neuropeptide Y (NPY), and pancreatic polypeptide (PP). These peptides possess antisecretory properties on the intestine. This effect can be blocked in vivo by neural antagonists, suggesting the intervention of neural receptors, although epithelial PYY-preferring receptors have been evidenced on jejunal crypt cells. The purpose of the present experiments was to compare the antisecretory properties in vivo of a series of PYY and NPY derivatives with various affinities for different Y receptor subtypes, in order to determine which subtypes were involved. A model of VIP-stimulated secretion by rat jejunal loops was used. The results were compared with the binding affinities for PYY-preferring receptors determined on rat jejunal crypt cell membranes. Full-length PYY(1-36) was about three times more potent than NPY(1-36), and 10 times more potent than PP in the low dose range. PP, however, had a low efficacy limited to about 50% inhibition of VIP effect. Both Y1 agonists ([Leu31, Pro34]PYY and [Leu31,Pro34]NPY), and Y2 agonists [C-terminal fragments ranging from PYY (3-36) and NPY(3-36) to PYY(22-36) to NPY(22-36)] displayed potent antisecretory properties. PYY derivatives and fragments were always more potent than their respective NPY counterparts. In contrast, Y1 derivatives and PP had very low affinity for the epithelial PYY receptor as measured in vitro by radioreceptor assay. These data suggest that the antisecretory effect of PYY/NPY/PP peptides in vivo involves the effects of several receptors: a Y2-like, PYY-preferring receptor identical to the epithelial receptor, a Y1-like receptor, and a third receptor with high affinity for PP.

M1 muscarinic mechanisms regulate intestinal-phase gallbladder physiology in humans

The contribution of muscarinic receptor subtypes to biliary control mechanisms is unclear. We investigated stimulated gallbladder function and release of associated hormones during M1-receptor blockade. Following a double-blind, randomized, crossover protocol, healthy volunteers each received placebo and telenzepine, a selective M1-receptor antagonist, as 2-h background infusion. Gallbladder contraction (by ultrasonography), bilirubin output, and release of cholecystokinin (CCK) and pancreatic polypeptide (PP) were assessed during increasing doses of endogenous (intraduodenal nutrient) and exogenous (hormonal) stimulation. All parameters were stimulated in a dose-dependent manner on placebo days. Contractile and secretory responses to low-dose caerulein (CCK analogue) were inhibited by 60-80% under telezepine, whereas high-dose (supraphysiological) stimulation overrode this effect. Similar inhibition was achieved during nutrient stimulation. CCK plasma levels rose during endogenous and exogenous stimulation but were unaffected by M1 blockade, whereas stimulated PP release was completely inhibited (> 100% decrease), reflecting suppressed vagal tone. Selective M1-receptor blockade inhibits the physiological response of the gallbladder in humans; this effect cannot be attributed to suppressed CCK release. Our findings support the hypothesis that CCK acts at the gallbladder via cholinergic nerves under physiological conditions. Viewed with our previous observations, nonselective antagonism of biliary function by atropine is primarily mediated through M1 muscarinic pathways.

The functional investigation of a human adenocarcinoma cell line, stably transfected with the neuropeptide Y Y1 receptor

1. The human adenocarcinoma cell line, HT-29, has been stably transfected with the cDNA sequence for the rat neuropeptide Y (NPY) Y1 receptor, and three Y1 clones (Y1-4, Y1-7 and Y1-16) have been isolated which express high levels of specific [125I]-PYY binding. We have studied the functional responses or lack of responses to peptide YY (PYY) and its analogues in the three transfected clones and HT-29 wild type (wt) cells. 2. Vasoactive intestinal polypeptide (VIP) produced long-lasting increases in short-circuit current (SCC) in both HT-29 wt cells and the Y1 clones. VIP EC50 values were 8.4-11.7 nM in all four cases. The elevation in SCC after a maximal concentration of VIP (30 nM) was significantly greater in Y1-7 cells than in either HT-29 wt epithelia or the other Y1 cell lines. 3. PYY (100 nM) and human pancreatic polypeptide (hPP; 1 microM) were ineffective in HT-29 wt cells under either basal or stimulated conditions. In contrast, basolateral additions of PYY reduced both basal and VIP-stimulated SCC in all three Y1 clones. After VIP, the PYY EC50 values (in nM) were 18.6 in Y1-4, 8.0 in Y1-7 and 52.5 in Y1-16 hPP (1 microM) produced only small and transient responses in each transfected cell type. 4. The Y1 receptor agonist, [Leu31, Pro34] NPY (1 microM) was also effective in the three Y1 cell lines. In the Y1-7 clone the EC50 value for the effect of this peptide was 149 nM, 18.6 fold less potent than PYY. 5. PYY and the Y1-selective non-peptide antagonist, BIBP 3226 displaced [125I]-PYY binding from Y1-7 cell membranes with Ki values of 2.0 and 3.1 nM respectively. In the Y1-7 clone, BIBP 3226 fully inhibited the reductions in VIP-stimulated SCC induced by 30 nM PYY, with an IC50 of 27.2 nM and 30 nM BIBP 3226 caused a parallel rightward shift on the PYY concentration-response curve, with an approximate pKB of 8.0. 6. HT-29 clones stably expressing the Y1 receptor therefore show responses to PYY and its analogues that are characteristic of that subtype, and the Y1-7 clone in particular will be useful in the assessment of novel Y1-specific drugs. This approach will also allow the functional study of NPY Yi receptors with selected mutations.

Regulation of hepatic insulin receptors by pancreatic polypeptide in fasting and feeding

Pancreatic polypeptide (PP) increases hepatic insulin receptor (IR) binding activity in fasted PP-deficient rats, but not fasted normal animals. PP-induced alteration of hepatic IR levels in normal animals may be detectable in the fed state when IR concentrations are lower than during fasting. In the current study, the effect of exogenous PP on IR concentrations in the fed and fasted states was determined in healthy 300- to 350-g male Sprague-Dawley rats. Ten animals were administered PP 100 microgram/kg/day for 3 days by intraperitoneal injection and 10 weight-matched control animals received saline vehicle. Five PP- and five saline-administered rats were fasted for 12 hr prior to organ procurement, while 5 PP- and 5 saline-treated rats were given free access to food for this period. Livers were removed and snap-frozen. IRs were isolated from solubilized hepatocyte membranes by affinity chromatography with agarose-bound wheat germ agglutinin. Western blots were performed using a specific antibody to the beta subunit of the IR, which was detected by a chemiluminescence technique after 45-min exposure to X-ray film. Exposed films were examined by scanning densitometry and IR concentration was expressed as absorbance units per milligram of hepatic protein (mean +/- SE). Statistical comparisons were by Student's t test with significance taken at P < 0.05. Feeding was associated with a significantly lower IR concentration in saline-administered animals compared with the fasted state (24.2 +/- 4.0 vs 53.3 +/- 11.1). PP administration in fed rats resulted in significantly increased IR concentration as compared with that seen in saline-administered fed animals (43.8 +/- 8.9 vs 24.2 +/- 4.0). This difference may be due to increased IR synthesis with long-term PP administration, and supports the role of PP as a regulatory factor in hepatic carbohydrate metabolism.

Broad spectrum antibiotic activity of the skin-PYY

Neuropeptide Y (NPY) and polypeptide YY (PYY) are two ubiquitous neuropeptides, found in brain and intestines, respectively, where they exert important regulatory functions. In this study, a new member of the YY family recently isolated from amphibian skin, skin-PYY (SPYY), is reported to inhibit irreversibly the proliferation of a broad spectrum of pathogenic microorganisms. NPY and PYY are shown to be endowed with the same activity. Their potency is similar to that of other antibacterial peptides which have been shown to exert their function by disintegrating the bacterial membrane. These findings and the fact that the C-terminal alpha-helical domain SPYY14-36, which is highly conserved among family members, was responsible for killing microorganisms and for permeation of phospholipid vesicles, suggested that the antibiotic activity may emerge via a membrane permeation mechanism. These findings also raise the question whether NPY and PYY exert in vivo a similar function in mammals.

Effect of the C-terminal tetrapeptide amide of gastrin (CCK-4) and pancreatic polypeptide on gastrointestinal electrical activity in the conscious miniature pig

The effect of IV infusion of CCK-4, 33.2 and 332 pM/kg/min, and pancreatic polypeptide (PP), 4.8 and 48 pM/kg/min, on gastrointestinal electrical activity was studied in conscious miniature pigs with electrodes implanted in the wall of the antrum pylori and small intestine. In the antrum pylori infusion of the higher dose of both peptides provoked an increase in frequency of the basic electrical rhythm together with a decrease in frequency of spike bursts. In the studied dose range CCK-4 and PP were without influence on small intestinal electrical activity.

Dose-responses for the slowing of gastric emptying in a rodent model by glucagon-like peptide (7-36) NH2, amylin, cholecystokinin, and other possible regulators of nutrient uptake

Several peptides have been proposed as regulators of nutrient release from the stomach and subsequent uptake from the gut. Using a phenol red gavage method, we compared the potencies of subcutaneously preinjected amylin, glucagon-like peptide-1 (7-36)amide (GLP-1), cholecystokinin octapeptide (CCK-8), gastric inhibitory peptide (GIP), glucagon, and pancreatic peptide on slowing the release of an acaloric gel from rat stomach. The latter three peptides did not fully inhibit gastric emptying at subcutaneous doses up to 100 micrograms. Amylin, GLP-1, and CCK-8 fully inhibited gastric emptying, with ED50s of 0.42 +/- 0.07, 6.1 +/- 0.12, and 8.5 +/- 0.20 nmol/kg +/- SE of log, respectively.

Pancreatic polypeptide, microinjected into the dorsal vagal complex, potentiates glucose-stimulated insulin secretion in the rat

Specific binding sites for circulating pancreatic polypeptide (PP) have been found within the dorsal vagal complex (DVC) in the caudal medulla oblongata. Therefore, the effects of rat PP on pancreatic hormone secretion upon its microinjection into the DVC in halothane-anesthetized rats at doses of 0.4-40 pmol were investigated. At this range of doses, the changes in plasma concentrations of insulin, glucagon and glucose over basal levels did not differ from those after vehicle microinjection. In a separate series of experiments, vehicle and PP at doses of 0.4 and 4 pmol were microinjected into the right DVC 40 min after the continuous infusion of D-glucose had been started. In animals receiving continuous infusion of D-glucose, PP microinjected into the DVC (4 pmol), resulted in markedly higher insulin levels at corresponding time points compared to those with vehicle microinjected into the DVC. These data indicate, for the first time, that microinjection of PP into the DVC may potentiate glucose-stimulated insulin secretion in halothane-anesthetized rats.

Pancreatic polypeptide stimulates gastric acid secretion through a vagal mechanism in rats

The present study examined the effect of pancreatic polypeptide (PP) on gastric acid secretion. A 45-min infusion of PP was delivered into the jugular vein of urethan-anesthetized rats. Rat PP (100 pmol) significantly increased acid secretion over baseline; bilateral cervical vagotomy or peripheral atropine both eliminated this acid response. Neither intraperitoneal infusion nor close intra-arterial infusion of 100 pmol PP into the gastric circulation altered acid secretion. These results suggest that although PP requires intact vagal reflexes to stimulate acid output, it does not act on afferent or presynaptic efferent terminals of the vagus or directly within the stomach. Given that vagal reflexes consist of an afferent limb, an efferent limb, and a central relay, it may be that the target of circulating PP lies within the central nervous system. Indeed, previous studies from our laboratory have shown that microinjection of PP into the dorsal vagal complex results in long-lasting vagal-dependent elevation of gastric acid secretion.

Effect of antrectomy and truncal vagotomy on erythromycin induced pancreatic polypeptide secretion

Erythromycin, a motilin agonist, enhances gastrointestinal motility but also stimulates endogenous pancreatic polypeptide (PP) secretion. We investigated whether the effect of erythromycin on PP release is dependent on (1) prokinetic activity of erythromycin generated from the antrum and (2) the long vagus nerve since erythromycin acts via cholinergic neurons. Erythromycin induced PP secretion was determined in 14 patients with antrectomy (6 patients with Billroth I type anastomosis, 8 patients with Billroth II type anastomosis), in 6 patients with truncal vagotomy and pyloroplasty but without gastric resection and in 8 healthy controls. Plasma PP levels in response to erythromycin (3 mg/kg i.v.) were determined at regular intervals for 180 min. Erythromycin induced a significant increase in plasma PP in the control subjects from 22 +/- 4 pmol/l (basal) to 49 +/- 4 pmol/l at 10 min. In the patients with truncal vagotomy plasma PP secretion after erythromycin was significantly (P < 0.05) increased (peak increment vs. basal: 98 +/- 10 pmol/l vs. 27 +/- 2 pmol/l) and prolonged compared to controls. In the patients with antrectomy no significant increases in plasma PP over basal were observed after erythromycin infusion. It is concluded that erythromycin stimulates PP secretion in healthy controls. The PP response to erythromycin is exaggerated after truncal vagotomy but absent after antrectomy indicating that the antrum is essential for erythromycin induced PP secretion.

Intracisternal rat pancreatic polypeptide stimulates gastric emptying in the rat

Pancreatic polypeptide (PP) has been shown to alter gastrointestinal functions, including increased gastric acid secretion and motility following brain stem injections of PP. The present study investigated the effect of an intracisternal injection of PP on the rate of gastric emptying. Additionally, the efficacy of the rat and bovine forms of the peptide was compared. Rats anesthetized with ether received an intracisternal injection of rat PP, bovine PP, or vehicle and, upon regaining consciousness, were fed a liquid test "meal." Intracisternal rat PP produced a marked enhancement in gastric emptying compared with control animals. Bovine PP, at doses equimolar to or three times greater than the effective rat PP dose, produced no change in gastric emptying. Pretreatment with systemic atropine prior to central injection of rat PP eliminated the stimulation of emptying, suggesting that PP acts through a cholinergic mechanism. When equimolar doses of rat or bovine PP were microinjected directly into the dorsal vagal complex, the region containing PP receptors, both were capable of stimulating antral motility. The response to bovine PP, however, was delayed and reduced compared with that seen following rat PP. The results suggest that rat PP strongly stimulates gastric emptying in rats and that bovine PP, depending on the route of administration, is either ineffectual or a weaker agonist for central PP receptors.

Pancreatic polypeptide microinjection into the dorsal motor nucleus inhibits pancreatic secretion in rats

BACKGROUND/AIMS

Pancreatic polypeptide (PP), a hormone released from the pancreas, inhibits pancreatic secretion in vivo but not in vitro, suggesting that the inhibitory action of PP on pancreatic secretion is indirect. Circulating PP in physiological concentrations binds to specific receptors in the dorsal vagal complex in the brainstem. Therefore, the hypothesis of this study was that PP acts centrally and inhibits pancreatic secretion by modulating vagal tone.

METHODS

The effects of microinjection of PP into the dorsal motor nucleus on 2-deoxy-D-glucose-stimulated and cholecystokinin octapeptide (CCK-8)-stimulated pancreatic secretion were examined in urethane-anesthetized rats.

RESULTS

Microinjection of PP to the dorsal motor nucleus but not brainstem sites outside it inhibited 2-deoxy-D-glucose-stimulated pancreatic flow and protein output. CCK-8-stimulated pancreatic protein output was inhibited by PP in the dorsal motor nucleus in dose-dependent and site-specific manners. The inhibitory effect of PP on CCK-8-stimulated protein output was eliminated by vagotomy.

CONCLUSIONS

The results suggest that PP acts in the dorsal motor nucleus to modulate vagal tone on the pancreas, thereby inhibiting pancreatic secretion. This study shows for the first time that the dorsal motor nucleus is involved in central feedback inhibition of the exocrine pancreas.

Pancreatic polypeptide stimulates gastric motility through a vagal-dependent mechanism in rats

The present study examined the influence of peripherally administered pancreatic polypeptide (PP) on vagal control of gastric motility. The jugular vein was cannulated in urethane-anesthetized rats and a strain gauge was sewn onto the antrum to monitor motility. Intravenous infusion of rat PP (2-200 pmol over 45 min) resulted in a dose-dependent increase in antral contraction amplitude. The motility response to i.v. PP was eliminated by pretreatment with atropine or bilateral vagotomy. In contrast to i.v. infusion, close intra-arterial infusion of PP into the gastric circulation had no effect on motility suggesting that PP does not act upon peripheral afferent terminals or directly within the stomach. These results support the hypothesis that circulating PP indirectly enhances gastric motility through a vagal cholinergic mechanism.

Intracisternal injection of TRH antibody blocks gastric emptying stimulated by 2-deoxy-D-glucose in rats

We evaluated the effect of 2-deoxy-D-glucose (2-DG) on gastric emptying of a non nutrient solution in conscious rats using a Phenol red method. Intravenous injection of 2-deoxy-D-glucose dose-dependently increased the rate of gastric emptying. This stimulatory action of 2-DG was abolished by subdiaphragmatic vagotomy. Intracisternal injection of thyrotropin-releasing hormone (TRH) antibody blocked intracisternal TRH and intravenous 2-DG-induced enhancement of gastric emptying but not the stimulation of gastric emptying induced by intracisternal pancreatic polypeptide. The TRH antibody injected intraperitoneally had no effect. These results suggest that endogenous TRH in the brain is involved in vagal-dependent stimulation of gastric emptying by 2-DG.

Pancreatic polypeptide inhibits calcium channels in rat sympathetic neurons via two signaling pathways

1. We studied modulation of N-type Ca2+ channels in adult rat superior cervical ganglion (SCG) neurons by pancreatic polypeptide (PP) using whole cell clamp. In large (> 20 pF) SCG neurons, PP inhibited ICa (35 +/- 2%, mean +/- SE) in a concentration-dependent fashion, with one-half maximal inhibition at 19 nM. 2. One-third of the inhibition was blocked by pertussis toxin, about one-half was blocked by N-ethylmaleimide (NEM) treatments, and about one-half was voltage dependent. The NEM-insensitive component of the PP inhibition was voltage independent and not significantly blocked by intracellular Ca2+ chelators. 3. The NEM-insensitive component was only weakly attenuated by GDP-beta-S, and moderately reversible with guanosine 5'-triphosphate (GTP)-gamma-S, in the whole cell pipette, leaving open the possibility that it is not mediated by a G protein. 4. Hence, PP inhibits ICa via two mechanisms: one G-protein-mediated and the other possibly G-protein independent. The former pathway is sensitive to pertussis toxin (PTX) and NEM, voltage dependent, and shared by several other transmitters in these cells. The latter pathway is PTX-and NEM-insensitive, not voltage dependent, and not affected by the presence of intracellular Ca2+ chelators.